1. Field of the Invention
The present invention relates to the melt spinning of multifilamentary yarn from synthetic organic polymer, and more particularly, to a spinnerette for use in a melt spinning process.
2. The Prior Art
In the melt spinning of multifilamentary yarn from synthetic organic polymer, the molten polymer is extruded with the aid of a spinning pump or some other device through one or more spinnerette orifices, each of which produces a filament. The continuous, molten filaments then pass through a quench zone where a stream of fluid such as air is passed across the path of the filaments to cool or solidify them.
Uniform, turbulence-free quenching of filaments is an important factor in the production of filaments having uniform physical properties, a prerequisite to acceptable performance of fibers in subsequent processes. This is difficult to achieve in a cross flow quench system, typically linked to a high throughput and high filament density melt spin process, as the transverse path of the quenching fluid causes it to contact first one side of the filament bundle and then pass therethrough. Those filaments most remote (downstream) from the entry of the quench fluid are cooled or solidified by a quench flow which has been preheated, made more turbulent and substantially diminished (via a downward moving boundary layer) by the obstruction presented by filaments closer to and previously contacted by the quench fluid. As a consequence, the cooling rate of the filaments is progressively slower as quench fluid passes through the filament bundle. In a staple spinning operation where the filaments have a modified, e.g., Y, cross-section, this effect is seen as higher fused filament level and lower modification ratio in filaments downstream of (more remote from) the quench fluid entry. Filament fusion results from collision of filaments prior to solidification and causes an undesirable fabric hand as well as uneven dyeing. The modification ratio of a Y-shaped filament is the ratio of the radius of the circle circumscribing the entire filament to the radius of the circle inscribed within the filament cross-section and excluding the legs of the Y. The uniformity of the modification ratio is an indication of the uniformity of quench. The modification ratio is higher for filaments cooled closer to the extrusion orifice (faster cooling rate), and the shape of the filament more closely approximates the shape of the spinnerette orifice; the more slowly cooled filaments have a lower modification ratio and the shape of the filament more closely approaches round.
The ideal solution to quench irregularity would be to increase the spacing of spinnerette orifices, resulting in increased distance between filaments for quenching. However, these are practical restraints to the increase in orifice spacing in a spinnerette of given diameter and orifice count. The prior art has attempted to solve quench irregularity by arranging spinnerette orifices in substantially "V" patterns (U.S. Pat. Nos. 3,293,696 to Bruni and 3,335,210 to Vinicki), concentric circles and crescent formations (U.S. Pat. No. 3,135,811 to Barnett et al.), rectangular grids, and irregular arrangements whereby the spinnerette orifices are staggered so that each one is located in the quench flow path without obstruction (U.S. Pat. Nos. 2,273,105 to Heckert and 3,280,424 to Heijnis). The closest prior art is believed to be U.S. Pat. No. 3,100,675 to Westerhuis et al. which discloses that it is essential that the spinnerette orifices be arranged in parallel rows, that the orifices in a given row be equally spaced, and that the distance between adjacent rows be less than the distance between the orifices in each row.